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vintage japanese mirror

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#1 lonn

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Posted 24 March 2019 - 10:33 PM

HI, Im building my first scope. I have found a 10in f4.5 orion mirror that's about 10 years old never used and made in Japan. Is this a good mirror and how does it compare to a 10in f5 GSO mirror. The price is about the same.I don't have $1000 to spend on a hand made mirror. My son and I doing this on a budget  using the stellafane plans. Thanks for any input that I get. 



#2 SeattleScott

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Posted 24 March 2019 - 10:50 PM

I don’t know that Orion ever had Japanese mirrors , much less just ten years ago. I would be highly suspicious of that. I can’t remember Orion making any F4.5 mirrors either. So something sounds wrong. I suspect either it wasn’t made in Japan, or more likely, it isn’t an Orion mirror (and probably wasn’t made in Japan either).

The Japanese love their refractors. They aren’t big Dob people. A 10” F4.5 Japanese mirror sounds like heresy to me. Not saying I couldn’t be wrong, but it sounds really fishy.

F4.5 will just about require a coma corrector, so add that to your budget. At F5 you could get away without one. F4.5 will be more demanding on collimation, eyepieces, coma, harder to get an excellent figure, etc. Unless the F4.5 is truly a premium mirror, I would go with the GSO at F5. Shoot I may go with the GSO regardless just because it is F5, particularly if you don’t have the budget for a coma corrector (or a full set of Vixen LVW eyepieces).

Scott

Edited by SeattleScott, 24 March 2019 - 10:55 PM.


#3 ngc7319_20

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Posted 25 March 2019 - 02:31 AM

HI, Im building my first scope. I have found a 10in f4.5 orion mirror that's about 10 years old never used and made in Japan. Is this a good mirror and how does it compare to a 10in f5 GSO mirror. The price is about the same.I don't have $1000 to spend on a hand made mirror. My son and I doing this on a budget  using the stellafane plans. Thanks for any input that I get. 

Given the information you have, I don't think anything can be concluded about the quality of the 10in F/4.5 "Orion" mirror vs. a 10in F/5 GSO mirror.  I flipped through my Orion catalogs from around that era, and did not see anything about 10in F/4.5 mirrors from Japan.  Their 10in scopes were F/4.7.  A 10 inch F/4.5 sounds more like a Meade scope to me, or something else.  As @SeattleScott said, the Japanese were not noted as big producers of mirrors.  Is there any way you can get the mirror to an expert to be evaluated before purchase?

 

I'm not sure of this, but you might have better chances replacing a bad quality GSO 10" F5 mirror, than a one-off 10" F4.5 mirror.  I presume you could just order another GSO mirror, or hopefully the vendor would just exchange it.  Perhaps you should ask the vendor about their return policy in case the mirror does not perform well -- maybe find a different vendor if they wont exchange or take back a bad mirror.  

 

As for the F/4.5 vs F/5 debate and Coma Correctors...  I don't think it matters at this level of interest...  A good quality F/4.5 or F/5 mirror will give wonderful views... Maybe someday if you are taking pictures through the scope you might want a coma corrector whether its F/4.5 or F/5.  I wouldn't worry about it now.  Good coma correctors go for $60 to $100 on the used market. 


Edited by ngc7319_20, 25 March 2019 - 04:09 AM.


#4 SeattleScott

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Posted 25 March 2019 - 09:39 AM

F4.5 sounds more like a decades old Meade or Coulter. The Meades have a pretty good reputation and mirrors typically go for $200-300. Heavy 2” thick mirror. Undoubtedly coatings degraded if not failing. Once I had my new 10” with enhanced coatings out next to a 10” F4.5 Coulter. The owner of the coulter was shocked at how much brighter views were through my scope. So if you get an old mirror, budget for a recoat. Otherwise you are hauling around a heavy 10” that performs more like a 6” or 8”.

I’m thinking the GSO is probably the easy choice here. Unless you want a coma corrector and a recoat.

Scott

#5 Don W

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Posted 25 March 2019 - 10:16 AM

You can't compare an unknown to a known. We have no information about the Japanese mirror other than where it was made. Does it say "Made in Japan" on it?

 

You can always have the mirror tested for quality by sending it to a mirror maker/coater or a club member that knows how to do a test. Then you have a known quantity to work with.



#6 lonn

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Posted 25 March 2019 - 08:29 PM

Ok, The ad is on e-bay. It says "Orion 10" f/4.5 Parabolic Primary Mirror" I asked him some questions. He wrote back. Purchased the mirror at the Orion store in Cupertino Ca about 10years ago. Paid over $400.00 that's 1/12 wave, Not sure that it was made in Japan but was very picky about this mirror. Wanted f/4.5 to have a shorter tube. He would use his mirror over the GSO mirror. Never built the scope the mirror has been stored in its box and is in excellent condition. So for a first time build, go with this mirror or the GSO mirrors?         



#7 SeattleScott

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Posted 25 March 2019 - 10:50 PM

Sounds very fishy. It’s not like Orion custom makes mirrors in California to a specific PV value. There are a lot of reputable mirror makers that could have done this, but Orion is not one of them. If it really is 1/12th PV then great. But more likely he just pulled it out of a 30 year old Coulter. Without an independent test report with a serial number matching the mirror, this really sounds like some guy feeding you a line to get a premium for his end of life mirror.

Scott

#8 ngc7319_20

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Posted 26 March 2019 - 12:43 AM

Is the mirror marked in anyway, or signed by the maker?  I would be very skeptical about any premium properties unless you know who made it.  Or if it has some test certification.  Otherwise it is likely to be mass produced mirror.    A premium mirror in this size with test documents would be around $2000.   If he was really "very picky about this mirror" he would know who made it, and have two independent sets of test documents for it.

 

Optics can be qualified by either the RMS or PV wavefront error.  Do you now which this mirror is?  A 1/12 wave RMS mirror is about 1/4 wave PTV, which is the about the lowest quality you will see advertised.  The GSO mirrors at Agena are described as "typically have a mirror surface quality of 1/16 wave RMS at least, and often better"... whatever that means with "typically... at least... and often."

 

Is the guy willing to take it back if you send it somewhere to be tested, and it is no where near 1/12 wave whatever?  Probably with Agena or some other vendor, there might be a chance to exchange it, if it is really bad.  Or you can easily buy another one for $300 or so.  I'm not aware of a source for cheap 10" F/4.5 mirrors.   Having it re-figured or re-ground would run $300 to $600. Maybe check around and have a "plan B" if it turns out to be bad.  Or build your scope in such a way that you can swap out the 10" F/4.5 and go to 10" F/5, if the first one is bad.



#9 dmgriff

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Posted 26 March 2019 - 11:25 AM

It is more than likely 1/12 wave RMS which was a standard manufacturers spec for mass produced asian mirrors. My "LightBridge Quality" GSO (Taiwan) 10in f/5 primary is spec'd at 1/16 RMS I think.

 

For comparison, I have a 6in f/8 nicely figured primary that tests at about 1/50 RMS and 1/10 wave PV.

 

Good viewing,

 

Dave


Edited by dmgriff, 26 March 2019 - 11:29 AM.



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